Factors affecting genetic connectivity and diversity of the island night lizard

Habitat loss and fragmentation is one of the most severe threats to global biodiversity. Because human development often fragments natural areas into habitat “islands”, studies which characterize the genetic structure of species isolated on oceanic islands may provide insight into the management of anthropogenic habitat islands. The San Clemente Island night lizard, Xantusia riversiana reticulata, is endemic to two California Channel Islands, each with a history of anthropogenic disturbance. We genotyped 917 individuals from San Clemente Island and Santa Barbara Island at 23 microsatellite loci to quantify population structure and identify natural and anthropogenic landscape features affecting intra-island connectivity. We found significant, but shallow, population structure on each island with sites < 400 m apart identified as distinct genepools. Landscape genetic analyses identified conductive habitat as California boxthorn and prickly pear cactus on both islands. Landscape features which decreased connectivity were unique to each island and included natural and human-mediated features. These results can inform management plans on each island by identifying habitat targets for mitigation and restoration efforts designed to improve connectivity. Our results highlight the need for considering fine-scale features correlated with contemporary and historical patterns of fragmentation, especially in small and isolated habitats on the mainland that may be analogous to oceanic islands.